fully define and use classes for composite structures

[abigailsnyder]

e.g. #14

rplzzz 38 minutes ago Member
This is a case where we could really benefit from defining classes for all of our composite structures. It would make describing what the functions are expecting easier, and we could even check the class attributes in functions that are expecting structures.

[rplzzz]

Another reason to do this is that we could define accessors for the components of the structures. As things stand, using fldgen in practice involves a lot of interactive use of str to try to figure out where the data you're looking for is located.